Electric heater



Jan. 6, 1942. F. E. FINLAYSON ELECTRIC HEATER Filed Dec. 18, 1940 hrwvewtow- Frank E. Finlagson,

His Attorney.

Patented Jan. 6, 1942 ELECTRIC HEATER Frank E. Finlayson, Ontario, Calif., assignor to General Electric Company, a corporation of New York Application December 18, 1940, Serial No. 370,705

4 Claims.

This invention relates to electric heaters, and it has for its object improvements in electric heaters of the sheath wire type.

More specifically, this invention relates to electric heating units of the sheath wire type, such, for example, as disclosed in United States Patent No. 1,367,341 to C. C. Abbott, dated February 1, 1921. In heating units of this type, a resistance conductor is enclosed by a metallic sheath, and is embedded in a compacted mass of granular insulating material, such as magnesium oxide, which holds the resistance conductor in spaced relation to the sheath. The insulating material may be compacted in any suitable way, as by swaging or rolling. To the ends of the resistance conductor are secured terminals which have their inner ends embedded in the insulating material, and their outer ends projecting from the sheath. In the construction of the heating unit, the resistance conductor with its terminals attached is temporarily secured centrally in the sheath for the operation of loading the sheath with the insulating material, and during the preliminary compacting operations. In most cases this has been accomplished by holding the outer ends of the terminals centrally of the sheath. One end of the sheath is closed, while the other end is open so that the granular insulating material may be loaded into the sheath. Then the insulating material is compacted.

Various structures have been provided for holding the terminals central. Usually these structures incorporated means for closing one end of the sheath, and providing an opening in the other end through which the insulating material may be introduced, even though the structure at this end holds the terminal therein central. One of these structures, which has been used extensively. comprises a washer for closing one end of the sheath; this washer has a central aperture through whichthe terminal in that end is thread ed so as to be held in the center of the sheath. This terminal has an outer head which prevents the terminal from being pulled into the sheath through the opening in the washer. The terminal at the other end has an eyelet in its outer end which receives an anchoring pin. The

' washer and pin are recer'ed in recessed seats provided for them in the respective ends of the sheath. These ends are peened over after the washer and pin have been placed in the seats so as" to hold the pin and washer in position. The spaces on each side of the pin provide openings through which the insulating material can be poured into the sheath. This terminal hold ing means necessitates terminals of different structure, one having a head on one end and the other an eyelet; this, of course, requires the stocking of two different terminals for every heater. Moreover, it is necessary to work the sheath to form the recesses in its ends, and also to peen the ends over so as to anchor the pin and the Washer.

Similarly, the other terminal holding structures used heretofore involved the use of different terminals at thetwo ends of the heater, or different holding means at the two ends, and holding means which is complex in its structure and dilficult to use, and also which generally involved expensive operations on the sheath.

This invention contemplates the provision of improved means for holding the terminals centrally during the loading of the sheath and the preliminary compacting operations which permits the use of terminals of exactly the same construction at the two ends, which avoids recessing the ends of the sheath, and which generally reduces the complexity of the operations of assembling the resistance conductor and terminals with the sheath, and consequently, reduces the expense of making the heater.

In accordance with this invention in one form thereof, each terminal is provided with a simple head on its outer end which may be formed by flattening the end of the terminal in any suitable way, as by means of a die. Cup-shaped members are provided with apertures in their bottoms through which the terminals are threaded. The cups are inserted into the ends of the sheath, and are prevented from moving inwardly too far by outwardly extending flanges on the cups which engage the ends of the sheath. The heads on the terminals prevent the terminals froni being withdrawn into the sheath through the openings in the cups. The cups may be rigidly clamped in the ends of the sheath by crimping the ends of the sheath, as by means of a simple die operation. One cup closes its end of the sheath, while the other cup is provided with openings in its bottom wall through which the insulating material may be poured into the sheath.

For a more complete understanding of this invention. reference should be hadto the ac ompanying drawing in which Fig. 1 is a frag- .oentary vertical sectional view of an electric sheathed heater provided with means arranged in accordance with this invention for holding the terminals and resistance conductor centrally within the sheath during the .ioadlng and. preliminary compacting steps; Fig. 2 is a fragmentary vertical elevation of the heater of Fig. 1, parts being shown in section so as to. illustrate certain details of construction, and-certain of the parts being shown in a more advanced stage in the process of making the. heating unit; Fig. 3 is a fragmentary view illustrating the upper end of the heater shown in Fig. 2 in a more advanced stage of the construction of the heater; Fig. 4 is a plan view of the section shown in Fig. 3; Fig. 5 is an enlarged plan view of one of the cups for holding one of the terminals; Figs. 6 and 7 are sectional views taken through the lines 6-6 and 11 respectively of Fig. 5 and looking in the direction of the arrows; and Fig. 8 is an elevation partly in section of a completed sheathed heater.

Referring to the drawing, this invention has been shown as applied to an electric sheath wire heater of the type disclosed in the abovementioned Abbott patent. As shown in Fig, 8, this heater comprises a helical resistance conductor I which is mounted within a metallic sheath II, and embedded in and held in spaced relation with reference to the sheath by a compacted mass l2 formed of any suitable heat conducting electrically insulating material, such as highly compacted granular magnesium oxide. The ends of the resistance conductor Ill are secured to terminals l3 and IE in any suitable manner, as by threading the end turns of the resistance conductor onto the terminals, as shown. The inner ends of the terminals are also embedded in the mass l2, and are held in spaced relation with reference to the sheath by the mass, while the outer ends .of the terminals project from the sheath, as shown. Preferably and as shown, the resistance conductor l0 and its terminals l3 and I4 will lie in the longitudinal center line of the sheath.

It will be understood that the sheath is being loaded with the magnesium oxide and while it is being swaged or rolled or otherwise acted upon to compact the magnesium oxide, it is necessary to provide'auxiliary means for holding the resistance conductor and the terminals centrally of the sheath.

In accordance with this invention, this means comprises a pair of cup-shaped members l and I6 arranged to be inserted in the ends of the sheath, as shown in Fig. 1, and having an outer diameter which is slightly less than the internal diameter of the sheath so that the walls of the cup fit fairly closely to the inner surfaces of the sheath. The cups at their outer edges are provided with outwardly extending flanges I5a and 6a which limit the movement of the cups into the sheath. The cup [5 is used to hold one terminal, for example the terminal l3, centrally of the sheath. and it is also arranged to provide openings through which the insulating material I! can be poured into the sheath. The other cup member l6 holds the other terminal member l4 centrally of the sheath, and also functions drawn into the sheath, andto prevent it from turning relative to the cup. The head 20 may be formed in any suitable manner, as by flattening the outer extremity of the terminal in any suitable way, as by means of dies. The bottom wall of the cup l5 also is provided with elongated openings 2| extending in opposite directions from the central opening l8 and positioned at right angles-to the grooves H3. The other cup member 16 is provided with a circular central opening 22 through which the terminal I4 may be threaded. Otherwise, the bottom of this cup is closed so as to close the lower end of the sheath. The terminal I4 is provided with a flattened head 23 similar to the head 20 on the other terminal to prevent the terminal from moving into the sheath.

In making the electric sheathed heater, the terminal M will be provided with its flattened head 23, and then the terminal will be assembled with its cup l6, as shown in Fig. 1. After this, the terminal M will be secured to its end of the resistance conductor [0, and the other terminal l3, which will have been provided with its head 20, will be secured to the other end ofthe resistance conductor Ill. The terminal l3, resistance conductor l0 and terminal M will then be threaded through the sheath H so that the cup l6 seats in its end of the sheath, as shown in Fi 1. The terminal I3 will then be withdrawn from its end of the sheath for assembly with its cup l5. It will be understood that the flattened head 20 will be threaded through the apertures 2| 1n the cup and then the cup will be turned 90 so as to bring the head opposite the grooves l9, after WhlCh the cup may be inserted in its end of the sheath with the head received in the grooves. The end of the sheath in which the cup 5 is mounted is then crimped, as by means of a square die, so as to rigidly secure the cup to the sheath. When the sheath is crimped,

parts 24 of the sheath will be offset inwar l the fashion shown in Fig. 2. It will be obs ei vell that these sections will incline the adjacent Walls of the cup, as shown in this figure, and, therefore, will become wedged between the inclined wall parts and the flange Mia. The upper end of the sheath is not crimped at this time.

I-he sheath is now ready for the loading operation, and for this purpose, the sheath is secured in an upright position in any suitable manner, and the insulating material is loaded into the sheath through the openings 2| in the cup l5. While the sheath is being loaded, it is intermittently tapped to settle the insulating material. The grooves l9 prevent th e head 20 from turning during the loading operation so as to obviate the possibility of the head becomi with the openings 2| and thereby p eir lt tl i terminal l3 to drop down into the sheath;

After the sheath has been loaded the end of the sheath which receives the cup [5 is crimped inwardly, as was the other end of the sheath so as to securely lock the cup in its position. I"his end of the sheath now has the shape shown in the plan view of Fig. 4. The areas of the compacted insulating material exposed thr openings 2l are painted with a suital l e alltg resin which hardens and prevents any of the insulating material from falling from the sheath during the subsequent compacting operations The heating unit is now ready for the coinpacting operation, and for this purpose the sheath may be elongated and reduced in diameteras by means of rolling or swaging. The

cups II and It not only hold the resistance conductor centrally within the sheath during the loading operation, but also during the preliminary swaging or reducing operations, that is, until the insulating material has become sufllciently compacted to hold th'se members central.

After the sheath has been reduced in diameter, the ends of the sheath, together with the cups and the terminal ends may be cut away so as to leave straight, exposed terminal ends, as shown in Fig. 8.

It will be observed that terminals of precisely the same construction are used. Also, the cups l and It may have the same preliminary construction, the cup l5 then being given its shape shown on the drawing by drawing out the bottom wall to form the seats 19, and by stamping out the openings 2i and I8 and drawing out the bottom wall to form seats l9. It is not necessary in making the heater to provide recessed seats in the ends of the sheath, or to peen over the ends of the sheath, or to perform other complex operations 'on the sheath. 7

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by letters Patent of the United States is:

1. The method of loading the sheath of an electric sheathed heater with a resistance conductor, terminals and powdered electrically insulating material which comprises providing a pair of cups of substantially the same preliminary construction adapted to be inserted in the ends of said sheath and having flanges for engaging the sheath to limit the movement of said cups into the sheath, forming openings in the bottom walls of said cups adapted to receive the terminals, assembling one of said cups with one of the terminals and forming a head on said terminal to prevent movement of the terminal through the opening in said cup, securing one end of the resistance conductor to said one terminal and seeming the other end of the resistance conductor to the other terminal, then forming a head on the other terminal, threading said other terminal/resistance conductor and said one terminal through said one end of said sheath so as to seat said one cup in said one end of said sheath and to bring the other terminal opposite the other end of said sheath, providing the other sheath to limit the movement of the cups into the sheath, forming openings in the bottom walls of the cups adapted to receive the terminals, as-

sembling one of the cups with one of the terminals and forming a flattened head on one end of said terminal to prevent movement of the terminal through the opening in said cup, securing the resistance conductor to the other end of said cup with an elongated opening through which 1 heater having a'resistance conductor mounted within a sheath and embedded in and supported in spaced relation with the sheath by a compacted mass of electrically insulating material,

and having terminals embedded in the insulating material and projecting from the sheath which comprises providing a pair of metallic cups adapted to be inserted in the ends or said sheath and providing on the cups outwardly extending flanges for engaging the ends of the terminal and securing the other end of the resistance conductor to one end of the other terminal, then flattening the other end of the other terminal to form a head, threading the other terminal, resistance conductor and said one terminal through said one end of said sheath so as to seat said one cup in said one end of said sheath and to bring the other terminal opposite the other end of said sheath, providing the other cup with an elongated opening through which said head on said other terminal may be inserted and then inserting said head through said opening and turning the cup to prevent withdrawal of the head through the opening and inserting the cup in the other end oi. the sheath, filling the sheath with said insulating material through said elongated opening, then highly compacting said insulating material into a hard dense mass, and then cutting away the end portions of said sheath including said cups and terminal heads.

3. The method of making an electric sheathed heater having a resistance conductor mounted within a sheath and embedded in and supported in spaced relation with the sheath by a compacted mass of electrically insulating material and having terminals embedded in the insulating material and projecting from the sheathwhich comprises providing a pair of metallic cups adapted to be inserted in the ends of said sheath and providing on the cups outwardly extending flanges for engaging the ends of the sheath to limit the movement of the cups into the sheath, forming openings in the bottom walls of the cups adapted to receive the terminals, as-' sembling one of thecups with one of the terminals and forming a flattened head on one end of said terminal to prevent movement of said terminal through the opening in said cup, securing the resistance conductor to the other end of said terminal, securing the other end of said resistance conductor to one end of said other terminal, then flattening said other end of said other terminal to form a head, threading said other terminal, resistance conductor and said one terminal through said one end of said sheath so as to seat said'one cup in said one end of said sheath and to bring said other terminal opposite the other end of said sheath, providing said other cup with an elongated opening through which said head on said other terminal may be inserted and then inserting said head through said opening and turning the cup to prevent withdrawal of the head through the opening and inserting the cup in the other end of the sheath, crimping said one end of said sheath so as to lock said one cup to said sheath, filling said sheath with said insulating material through said openings in said other cup, crimping said other end of said sheath to lock said other cup to said sheath, and elongating and reducing said sheath so as to highly compact said insulating material.

4. The method of loading the sheath oi. an

5 electric sheathed heater with a resistance conductor, terminals and powdered electrically insulating material which comprises providing a pair of cups of substantially the same prelimi nary construction adapted to be inserted in the ends of said sheath and having flanges for engaging the sheath to limit the movement of said cups into the sheath, forming openings in the bottom walls of said cups adapted to receive the terminals, assembling one of said cups with one of theterminals and forming a head on said terminal to prevent movement of the terminal through the opening in said cup, securing one end of the resistance conductor to said one terminal and securingv the other end of the resistance conductor to the other terminal, then forming a head on the other terminal, threading said other terminal, resistance conductor and said one terminal through said one end of said sheath so as to seat said one cup in said one end of said sheath and to bring the other terminal opposite the other end of said sheath, providing the other FRANK E. FINLAYSON. 

